What Sherlock knew - PotterlockJohnlock AU
by moriartime
Summary: Sherlock, incarcerated in Azkaban's highest security cell. John, his oldest and only friend, looking for answers. How did the world's most famous Auror fall from grace? To find out, John must unbury secrets and lies that have been dead for too long. To find the truth, Sherlock and John must take a journey to where it began... Hogwarts.
1. Chapter 1 (06-19 04:37:52)

**Introduction**

Sherlock Holmes, incarcerated in Azkaban's highest security cell. John Watson, his oldest and only friend, looking for answers. To find the reasons behind what Sherlock did, John must unbury secrets and lies that have been long dead. How did the most famous Auror of his time fall from grace? John, and John only, is the key to the answer. And, to find it, they need to take a journey back to where it all began. Hogwarts.

 **Chapter One**

Sherlock knew.

Of course he knew - he knew everything. But what he didn't know was _why_.

His cell wasn't good for many things - it was small, damp, his punishment manifested into stone walls and a thin iron bedstead. However, the corridor outside (which led to many other cells, each containing wizards in varying degrees of sanity, but none as sane as he was, he believed) had been enchanted so that every tiny sound made was magnified to ten times the original amplitude. The guards had done it, so that, in the event of an escape, they would hear the slightest scuffle and come running.

Therefore Sherlock's cell was remarkably good for listening. So, when he heard him walking up the corridor towards his cell, he was able to know many things at once.

The man was short, his footfalls not very far between, marking him as being about five foot six. The soles of his shoes were worn from endless pacing - a nervous habit, given away by the softness of his steps.

Lastly, the distances between his left and right step were different, meaning that, though he had long recovered from a psychosomatic limp, the memory of his war days resurfaced when he was about to visit the very man who had told him that his limp was, in fact, psychosomatic.

That man, obviously, was Sherlock.

The walker finally stopped at the end of the corridor, outside Sherlock's cell (because apparently, Sherlock was the most dangerous prisoner in the corridor, and had to be kept furthest away from the fire exit in case he escaped). Leaning against the iron bedstead, his back to the door, the silhouette of Azkaban's most dangerous criminal pressed his fingertips together underneath his chin.

"Hello, John," Sherlock said.


	2. Chapter 2

**Chapter Two**

John wasn't sure what changed the day he decided to visit Sherlock.

Maybe it was Mary who finally persuaded him - she could be very strong-willed sometimes. Or perhaps he was just sick with nostalgia - sometimes he would stand in his fireplace, his hand full of floo powder, and a stray thought would whisper in his ear: _Why don't you go to Baker Street? Just to see how it's changed?_ But John knew that he would never find Sherlock there, despite the foolish part of him that wanted it. His voice would crack before he could complete the words; the furthest he'd ever got was "Bake-". Then he'd say, "The Ministry of Magic", and he would appear there, just like he was supposed to.

John hated it.

Whatever had moved him to visit Sherlock, there was another part of him - the more sensible part - which made him want to turn back a thousand times. John disapparated from his house, then he nearly got himself splinched by almost changing his mind. He used his status as a Ministry worker to negotiate his way past the dementors, then he'd take his wand out in paranoid self-defence. He asked for directions to Sherlock's cell, then his voice would crack.

John decided that walking down that corridor, flanked on either side by silent dementors, was the worst part. His foot would freeze in midair, and he would have turned back, had it not been for his terrifying escorts.

Sherlock didn't turn around when John approached his door. (Thanks to a few enchantments that Mary had cast on his eyes before he'd left, he could see through it. John thought for a second that he wasn't real, given the image was so hazy. But when he spoke, John decided that he was very real.)

"Why now?" Was all Sherlock said.

"Why ever?" Was all John said. He knew better than to express his surprise that Sherlock knew it was him. Those days of ' _how did you know that?'_ and _'what an amazing deduction'_ were over.

"You want the answers. You've always wanted answers," came his reply. Despite the picture being unclear, his voice sliced through the door like a butterknife.

"Of course I want answers, Sherlock." His fined tuned nonchalance was annoying John already. It made his skin prickle with heat. "Did you think I just popped in for a _chat_? To play cards?"

"One thing you shouldn have learned from our time together is that there's never just one answer." He turned around now, and John flinched inwardly - at both the familiarity of his face and the features time had given to him that made him a stranger.

John cursed. "And you know I'll always listen to them all."

They were silent for a moment - Sherlock, incarcerated in this cell, and John, wishing he were closer to him and hating himself for it. Then John said, his voice quieter than before, "Where did it begin? At least tell me that."

"Hogwarts. Like everything does." The dull light of the cell played shadows across his face, making the holes of his eyes, the hollows of his cheekbones, seem even deeper.

Suddenly Sherlock looked John dead in the eyes, and John saw it like it was yesterday. _He was in that field again. He stood back, the fog curling around his feet, leaving a clearing with two figures._ _Sherlock, and another boy, clad in a Ravenclaw scarf. Silver. Blue. A flash, a curse, a death. Lifeless eyes stared at the sky, and there was a scream, but John couldn't tell whom it belonged to, but it was an alarm, carrying on and on and-_

Dragged back to the present, John, clutched the cold wall for support, sweat running in rivulets down his neck, gasping. "What was that? Sherlock, what did you do?"

The criminal was calm. "That was a memory."

"You..." John fought to compose himself. Suddenly his robes felt like snakes, suffocating him. "You have my memories? Sherlock?"

This wasn't what John had expected to find, inside that high security cell, inside Sherlock. But it was him all along. _Sherlock_ was the one who had taken his memories.

And they were the answers.

John gulped, his face a picture of buried bravery. "You can't tell me, can you? But you can show me."

Sherlock nodded once. That was when a part of John, the part that had taken him here in the first place, whispered to him: _I'm ready now. Show me who you are._


	3. Chapter 3

**Chapter 3**

 **A/N: Firstly, I just want to thank Fizz the Great for the lovely review! This chapter's for you; I hope you enjoy it. :):)**

"Give me your wand, John," Sherlock said calmly, "So I can give you your memories."

John nervously held it out, feeling the cool wood kiss his hand. "My wand, in exchange for my memories. How diplomatic of you."

"Do you want to know, or not?" Sherlock retorted, as John made a gesture to hand him the wand through the door. Then, so quickly it was as if it hadn't moved at all, the dementor on John's right stood between him and the door. _Stood_ wasn't the right word, John mused. Dementors did not walk like living men. Perhaps it simply _was,_ and always had been.

Either way, it wasn't moving.

In a fleeting moment, John knew that he would risk anything to get his memories back. He realised how much Sherlock was to him, and it scared him, because he realised he would do _anything_ for him. After all this time, John would rather be locked up with him, than have to face a door between them.

"EXPECTO PATRONUM!" He flung his patronus into the darkness - chaos followed. He could hear the anguished screams of the dementors as if they were inside his very head; he dropped his wand to the floor with a clatter, then kicked it in what he hoped was the direction of Sherlock's cell, willing it to slide under the door into his friend's hands.

Sure enough, a crack forged itself down the middle of the stone door with a bone-shaking crunch. Sherlock had found John's wand, and was throwing curses at the door with surprising power for someone who hadn't practised magic for...eleven years? Twelve?

(John wasn't surprised at all. If he allowed himself to be surprised every time Sherlock did something extraordinary, he'd have gone crazy by now.)

The door shook once. It then exploded from the inside, pieces of cement raining down on John and skidding across the floor. Quick as a flash, Sherlock was by his side, and they were racing down the corridor, leaving bedlam in their wake for the first time in eleven or twelve years.

Just like old times.


	4. Chapter 4

**Chapter four**

John wasn't sure what he was expecting the day he decided to visit Sherlock. He sure wasn't expecting an emotional reunion. Neither was he expecting to help his friend be the first prisoner to escape from Azkaban since Sirius Black himself.

 _Give me my wand, John._ And he had done just that. But he hadn't just given Sherlock his wand that day; he'd sacrificed his job, his freedom, and his identity. John envisioned some kind of half-life as a wanted fugitive after this.

Now he wanted just one thing back from Sherlock: answers. _I helped you get out of here, so now tell me how you got in in the first place._

But the first thing John did as a wanted man was not to press him for answers. Instead, after they had cleared Azkaban's no-apparation zone, he grabbed Sherlock's arm and took them to the first place he could think of.

"...Are we in Speedy's café?" Sherlock's usually monotone voice held a trace of wonder. They materialised in the lunch queue, next to a muggle couple who stared, slack-jawed. John snatched his wand from Sherlock and murmured, "Obliviate."

"First place I thought of. Don't know why," he explained, getting his bearings. The silver tables covered in ketchup stains, the greasy linoleum floor, the smell of grilled cheese... John welcomed the change from the stale prison air.

They took seats right at the back, not ordering anything. No words were spoken - John was trying to separated the old times from this twisted reality. Images burned on his eyelids - Sherlock, the Ministry's only consulting Auror; John, his willing companion. Then _this_ \- Sherlock, his face gaunt and grey, a half-dead criminal; John, scared, confused.

Suddenly Sherlock reached out to touch John's face. His fingers were cold, rough. "You're older."

"Do you have any idea what all those years did to me?" John broke off before his voice cracked. "Not knowing. Not knowing _why,_ Sherlock."

Sherlock dropped his hand, letting it rest on the table. "Guess that would age one a bit."

"No sh-" The clatter of plates from the kitchen drowned out whatever John had said.

"Do you realise," Said John, after a moment of weighted silence, "that we're on the run now?"

"Until we die, or get caught. Don't act like its the first time." Sherlock smirked beneath his stubble. Then he sighed, suddenly deflated. "I guess it's time to give you those memories of yours."

"It is." It wasn't as if John had lost _all_ his memories - he still remembered meeting Sherlock in first year (not even the most skilled wizard could make him forget _that_ in a hurry), their adventures at school, how he'd got his job at the Ministry and followed Sherlock to consult the most dangerous crimes in the wizarding world.

But there was a gap that John had never been able to explain. It was as if, some time in their sixth year, his mind had glossed over something important. All John knew was that something momentous had happened then, but it was out of his reach. And it had something - no, _everything_ \- to do with why Sherlock had spent the last eleven or twelve years in Azkaban.

He was in Speedy's again, and Sherlock had his wand. And he was pressing it against John's temple.

John shut his eyes and remembered.

 _He'd been in this room before. Four beds stood at the walls, covered in blue and silver scarves, black robes and brightly coloured sweet wrappers. Sherlock's bed was different. It was bare and white, not a colour in sight. The only notable feature was a small cauldron at its side, brimming with a silver liquid._

 _Was is silver? Or was is pure light; every colour at once? John seemed to forget himself every time he looked into its depths._

 _"I don't want to do this," He heard himself say. His voice was young and tremolous._

 _"This knowledge could put you in danger, John," came another voice from beside him, belonging to Sherlock. "You could be tortured. Imprisoned."_

 _"But we both know that's not why you're doing this," John turned to him, his eyes full of stinging accusation. "You don't trust me." It was cruel; he knew that. Because he knew that Sherlock was incapable of such a thing._

 _It was only when he turned to look at his friend, that he saw what Sherlock_ could _feel: fear. "This isn't..." His eyes glistened; his voice was like a string pulled taught, about to snap. "This isn't your fight. Please,"_

 _"But we can fight this together!" John burst out. "You're putting yourself in danger - at least let me_ help _you, Sherlock..."_

 _That was when John was tackled to the ground - a simple spell bound his hand and feet. "Sherlock, what-" he gasped._

 _"I'm sorry, John." Sherlock had his wand. And he was pressing it against John's temple, slowly stealing his memories._

 _The last thing John saw before blacking out was the silver contents of the Pensieve, swirling and spiralling, as if they had been hungry, and were about to be fed._


	5. Chapter 5

**Chapter five**

Now John was gasping for air, his mind reeling. A few muggle diners were eyeing him cautiously over their sandwiches. "Damn you, Sherlock," he said through gritted teeth.

Sherlock didn't reply; he just looked kind of sad. "Are you ready for more?"

"Of course I bloody am." But John was sweating. He wasn't sure if he was able to stand up. Sherlock raised a sceptical eyebrow at him, then John grabbed his wrist and pressed his wand to his own head again.

 _September, 1975. John Watson, a stocky third year, sat in the window of his dorm, his red and gold quidditch robes wrapped around himself for comfort._

 _"Don't you want to meet him?" A voice floated up from the common room._

 _"Sherlock!" John nearly fell off his seat in his attempt to get up. "What are you_ doing _here?"_

 _"The Fat Lady's useless," grinned Sherlock, now leaning on the doorframe, his Ravenclaw tie glinting in the firelight. "She'll let anyone in with a Peruasion charm up their sleeve. So...do you want to meet my brother or not?" He demanded impatiently._

 _John suddenly had a terrifying. image of Mycroft, the pompous_ _seventh year Prefect, gazing at him haughtily from above. He involuntarily shuddered. "Not_ that _one," corrected Sherlock, as if he'd read John's mind. "The other one. The new one."_

 _Ah! Now it made sense. John dimly recalled the events of the previous evening - the warm glow of the feast, the endless sorting, Dumbledore's booming speech. And another Holmes brother._

 _John guiltily hoped he was more like Sherlock than Mycroft. As soon as he'd had the thought, he felt his cheeks heat up. "Where is he?"_

 _"Right here." Came a small, firm voice from behind Sherlock. Had he been here all along? He'd been awfully quiet. "Tom Holmes. But I like to go by Tom Riddle." The small boy, waxy and pale, had Sherlock's dark hair and Mycroft's eyes, the irises swallowed by black._

 _"Why Riddle?" Was the first thing that John said._

 _"I like playing pretend." Was all Tom Riddle said, sticking out his hand for John to shake, a ghastly smirk playing across his features._


End file.
